General System Description

Distributor Ignition (DI) System:

PURPOSE
The distributor ignition system controls fuel combustion by providing a spark to ignite the compressed air/fuel mixture at the correct time. To provide improved engine performance, fuel economy, and control of exhaust emissions, the Powertrain Control Module (PCM) controls distributor spark advance (timing) with an Ignition Control (IC) system.

TIMING CONTROL
To properly control ignition and combustion timing the PCM needs to know:
^ Camshaft position.
^ Engine speed (RPM).
^ Engine load (manifold pressure or vacuum).
^ Atmospheric (barometric) pressure.
^ Engine coolant temperature.
^ The amount of detonation.

OPERATION
Timing Control
The distributor ignition system is a net build distributor (no timing adjustment) that provides angle based timing information to the PCM for individual cylinder spark timing. The ignition module is capable of providing both 4X and 18OX timing pulses each crankshaft revolution. Using these timing pulses, the PCM processes ignition spark timing and sends an IC signal to the ignition coil module to activate the secondary ignition system.

Ignition Control Module
The PCM provides power, ground, and two 5 volt reference voltages to the ignition control module. As the camshaft turns (during crank or run), a slotted two-track timing disk is rotated inside the ignition control module. Each time a slot in either track of the disk is properly aligned, the ignition control module will pulse one of the 5 volt reference voltages to ground.

Reference Signal
A reference signal is generated each time the PCM detects that the reference voltages have been grounded by the ignition control module. When the PCM detects reference signals, ignition timing can be processed.

4X and 18OX Signals Compared
The PCM will also compare the 4X and the 18OX signals to each other to determine the location of the number one cylinder and top dead center. In addition, if only one signal is being received by the PCM, a Diagnostic Trouble Code (DTC) will be set. Diagnostic Trouble Code 16 Distributor Ignition System (Low Resolution Pulse) will be set if the 4X signal is missing and Diagnostic Trouble Code 36 Distributor Ignition System (High Resolution Pulse) will be set if the 18OX signal is missing. The vehicle will not run if the 4X (REFERENCE) signal is not available at the PCM for processing.